Many years ago, I was going to see the play "Wait Until Dark" (Marisa Tomei and Quentin Tarantino were in the play the time, neither of them very good, but that's besides the point).
I mentioned to my Mom that I was going and she said "Oh, is that the one where he uses the light in the refrigerator at the end?"
"Gee, thanks. I don't know. I've never seen it before."
I spent the play looking at that damn refrigerator waiting for the spoiler.
Anyway, someone going to see a murder mystery has no business researching it online except for maybe reading reviews of known publications if they must. If they look at the Wikipedia article or discussions of the work somewhere else, then it's their own fault for getting spoiled...